1. Field of the Invention
The present invention relates to a crane and a boom hoisting device of the crane, permitting easy removal of a mast or a gantry for raising and lowering a boom attached to a body frame.
2. Description of the Related Art
The related art will be described below with reference to FIG. 4 showing a crawler crane as an example.
This crane has a body frame comprising a lower travel body 1 of a crawler type and an upper rotating body 2 mounted on the lower travel body 1 so as to be rotatable about a vertical axis.
The upper rotating body 2 is basically composed of a boom 4 mounted on a rotating frame 3 as a base, three winches 5, 6, 7 as main hoist, auxiliary hoist and boom hoisting winches, respectively, and a mast 8 for raising and lowering the boom 4.
A base end portion 8a of the mast 8 is attached to a front side portion 3a of the rotating frame 3 so as to be pivotable about a horizontal axis and attached detachably to the front side portion 3a of the rotating frame 3. In order to avoid mutual interference of wire ropes delivered from the winches 5 to 7, these winches are mounted at intervals on the rotating frame 3 in the order of main hoist winch, auxiliary hoist winch and boom hoisting winch from the front side.
As shown in FIG. 4, a hoisting wire rope 12 of the boom hoisting winch 7 is stretched through an upper spreader 9 provided at an upper end portion of the mast 8 and is spread like a rattan blind on both a sheave of the upper spreader 9 and a sheave of a lower spreader 10 mounted on a rear portion of the rotating frame 3. Thus, when the boom hoisting winch 7 is operated to unwind or wind the hoisting rope 12, thereby changing the distance between the upper spreader 9 and the lower spreader 10, the mast 8 rises or lowers, so that the boom 4, which is connected to the mast 8 through a guy line 11, also rises or lowers.
As another upper rotating body, as shown in FIG. 5, one provided as a substitute for the mast 8 with a gantry 30 having a gantry compressing member 31 and a gantry pulling member 32 is known (see, for example, Japanese Registered Utility Model No. 2542385).
In the gantry 30 shown in FIG. 5, a base end portion 31a of the gantry compressing member 31 is connected to a front side portion of the rotating frame 3 and a base end portion 32a of the gantry pulling member 32 is connected to the rear side portion of the rotating frame 3 each pivotably in the hoisting direction. At a gantry top 33 to which front end portions 31b and 32b of both members 31 and 32 are connected in a relatively pivotable manner there is provided a gantry-side spreader 20. A guy line 22 is connected at one end thereof to a front end of the boom 4 and a guy line-side spreader 21 is connected to an opposite end of the guy line 22. A wire rope 47 drawn out from the boom raising/lowering winch 7 is spread on both spreaders 20 and 21. Therefore, when the boom hoisting winch 7 is operated to unwind or wind the hoisting rope 47, thereby changing the distance between both spreaders 20 and 21, the boom 4 rises or lowers. In FIG. 5, the numeral 23 denotes a mounting portion for mounting the boom 4, numeral 5 denotes a main hoist winch, and numeral 6 denotes an auxiliary hoist winch. In FIG. 5, the same portions as in FIG. 4 are identified by the same reference numerals as in FIG. 4.
Further, as described later, there is known a crane of the construction wherein both mast and gantry are used in combination and the mast is raised and lowered by the gantry to raise and lower a boom.
When moving to a work site, this crane is dismantled for transport by a trailer or the like. This dismantling is performed so as to satisfy the transport weight allowed for the trailer or the like.
For reducing the transport weight in the above upper rotating body, the boom which is heavy and a counterweight are removed of course. Besides, in a large- or ultra-large-sized crane having a very heavy upper rotating body, there sometimes is a case where it is necessary to remove a mast or a gantry.
However, since a hoisting wire rope connected to the boom hoisting winch is spread on the mast or the gantry, there has been the problem that the removal and mounting of the mast and the gantry are troublesome. More particularly, for removing the mast or the gantry it is necessary to pull out the hoisting wire rope and thus a very troublesome work requiring a long time is needed. Conversely, when mounting the mast or the gantry, it is necessary to pass the hoisting wire rope therethrough and thus here again a very troublesome work requiring a long time is needed.